The report concluded that that defensive gun uses (DFU) was wildly overestimated because of the problematic self-reporting methodology used. As the report noted at pages 8-9:

Each of the respondents in the NSPOF was asked the question,"Within the past 12 months, have you yourself used a gun, even if it was not fired, to protect yourself or someone else, or for the protection of property at home, work, or elsewhere?" Answers
in the affirmative were followed with "How many different times did you use a gun, even if it was not fired, to protect yourself or property in the past 12 months?" Negative answers to the first DGU question were followed by "Have you ever used a gun to defend yourself or someone else?" (emphasis in original). Each respondent who answered yes to either of these DGU questions was asked a sequence of 30 additional questions concerning the most recent defensive gun use in which the respondent was involved, including the respondent's actions with the gun, the location and other circumstances of the incident, and the respondent's relationship
to the perpetrator. Forty-five respondents reported a defensive gun use in 1994 against a person (exhibit 7). Given the sampling
weights, these respondents constitute 1.6 percent of the sample and represent 3.1 million adults. Almost half of these respondents reported multiple DGUs during 1994, which provides the basis for estimating the 1994 DGU incidence at 23 million. This surprising figure is caused in part by a few respondents reporting large numbers of defensive gun uses during the year; for example, one woman reported 52!...
The results still suggest that DGU estimates are far too high. For example, in only a small fraction of rape and robbery attempts do victims use guns in self-defense. It does not make sense, then, that the NSPOF estimate of the number of rapes in which a woman defended herself with a gun was more than the total number of rapes estimated from NCVS (exhibit 8). For other crimes listed in exhibit 8, the results are almost as absurd: the NSPOF estimate of DGU robberies is 36 percent of all NCVS-estimated robberies, while the NSPOF estimate of DGU assaults is 19 percent of all aggravated assaults. If those percentages were close to accurate, crime would be a risky business indeed! NSPOF estimates also suggest that 130,000 criminals are wounded or killed by civilian gun defenders. That number also appears completely out of line with other, more reliable statistics on the number of gunshot cases.
...
The reason this sort of bias can be expected in the case of rare events boils down to a matter of arithmetic. Suppose the true prevalence is 1 in 1,000. Then out of every 1,000 respondents, only 1 can possibly supply a "false negative," whereas any of the 999 may provide a "false positive." If even 2 of the 999 provide a false positive, the result will be a positive bias—regardless
of whether the one true positive tells the truth. Respondents might falsely provide a positive response to the DGU question
for any of a number of reasons:

• They may want to impress the interviewer by their heroism and hence exaggerate a trivial event.
• They may be genuinely confused due to substance abuse, mental illness, or simply less-than-accurate memories.
• They may actually have used a gun defensively within the last couple of years but falsely report it as occurring
in the previous year—a phenomenon known as "telescoping."